Fish oil may improve triglyceride concentrations in patients with various renal diseases. The mechanism is unknown but may involve an alteration in clearance kinetics associated with VLDL, the primary lipid transport particle. Since abnormalities in triglyceride metabolism are very common in patients with nephrotic syndrome, this study evaluated whether a diet enriched with fish oil compared with an isocaloric diet enriched with olive oil improves triglyceride concentrations, and whether it does so through an alteration in VLDL particle kinetics. VLDL kinetics were measured after 5 weeks of either 9 grams of fish oil in the diet or 9 grams of olive oil in the diet in subjects with nephrotic range proteinuria. VLDL particle apo B-100 protein was labeled with a stable isotope of leucine (15N-leucine) by the flooding dose technique. Serum was harvested in a standard pharmaco-kinetic pattern over 2 weeks to determine the rate of appearance (Ra) and rate of disappearance (Rd) of labeled VLDL apo B-100 protein.Patients with nephrotic syndrome often have abnormalities in lipid metabolism. These may arise from increased synthesis of lipoproteins by the liver. This study is designed to test the effect of a dietary adjustment using fish oil versus olive oil (isocaloric diets) to examine the effect of dietary lipid composition on the synthesis of VLDL using a stable isotope, N15-luecine, as a tracer of VLDL kinetics and metabolism in subjects with nephrotic syndrome who consume a fish oil or olive oil enhanced diet for 6 weeks intervals.